I would like to take part in three local cyclocross races in the coming weeks but have a bike dilemma:

Should I convert my track frame to a new fork and put one cantilever brake on it and change the tyres, or change the tyres on my Kona road bike (I checked to be sure that there is enough clearance for cross tyres) and race with road bike style calipers but increase the calipers clearance to the rims? At the moment putting cross tyres on my road bike is the cheapest but no one uses calipers so I assume it's a stupid idea. But is converting the track bike silly too? All races are flat, btw.

IMHO, a track frame has a geometry that is very different to that of a "real" cross bike. Also, most track frames are built for a very different kind of stress, as track surfaces tend to be even. The last point is also partially true for road bikes. And try to find out if you're even allowed to ride with only one brake (track frame).
–
arneOct 10 '13 at 12:53

Keep in mind that you can swap your fixed cog with a freewheel (you'll probably want one with a nice easy ratio). A freewheel will thread on to your fixed gear hub, even if it's not a flip flop. I do this on my hardcourt polo bike with no problem.
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BenzoApr 8 '14 at 14:43

I'd have to say both sound like a pretty bad idea, with the fixie hard to mount/dismount and control in a cyclocross type situation. Sheldon brown does mention someone whose done it (http://sheldonbrown.com/singlecross.html), but it seems like something you may want to do after considerable practice with the course in a non-fixie. You wouldn't be the first person to try it though (http://www.fixedgeargallery.com/interviews/mike_clark/). As for a road bike, I'm not sure you want to put your road bike through a cross race. If its not too muddy and your road bike is set up with a stable geometry, you may come out alright with the road bike. I'd say if you have downtube shifters though, you will need to move to barend shifters or brifters or retroshift or something (you didn't say which Kona bike you had - they currently do a wide range of them and I have seen a Honky Tonk with downtube shifters for some reason...).

My suggestion is to pick up an old rigid mountain bike (say, a 80s-90s specialized rockhopper/hardrock) which should be pretty cheap and easy to come by, put some tires (look at some cross tires you were considering in 700c and find something which you think will be similar in 26) and decent brake pads and go for it. Lots of people use mountain bikes for beginner cross, and I think this option will probably keep your road bike in better condition and not be too different in price from the first option depending on which rigid mountain bike you start with.

If your road bike will fit a cross tire, then I'd just use that. 30 years ago when "long reach" calipers were standard, it was fairly common to use caliper brake bikes for cross. It's not ideal, but it will work as long as the course isn't super muddy.

However, most road frames these days will only work with at most a minimal tread 28mm tire. There aren't many cross tires that would fit in "standard reach" brakes.

Even if you go with a fixed gear setup, I think you really want two brakes for riding dirt. By the time you convert the track bike, you're pretty close to what a used rigid MTB would cost. I have not raced cross with a fixed gear, but I've done a fair bit of dirt riding on a fixed gear ( see http://www.63xc.com/ ) and you really need a back brake that doesn't skid.